1. Field of the Invention
The invention generally relates to a start control device for a vehicle in which an automatic transmission is installed, and, more particularly, to a start control device of the vehicle in which neutral control is performed.
2. Description of Related Art
The automatic transmission installed in the vehicle is connected to the engine via a torque converter, or the like, and has a speed changing mechanism having a plurality of power transmission paths. The automatic transmission is arranged to automatically switch the power transmission paths, or automatically change the speed ratio or gear position, based on, for example, the accelerator pedal position and the vehicle speed. Generally, the vehicle having the automatic transmission is provided with a shift lever that is operated by the driver. In operation, the shift lever is operated so as to establish a shift position or range (for example, reverse drive position, neutral position, forward drive position, etc.) based on the selected position of the shift lever, and automatic shift control is performed within the range of the thus established shift position (which is normally the forward drive position).
When the vehicle having such an automatic transmission is in a stopped state with the forward drive position being established, driving force is transmitted from the idling engine to the transmission via the torque converter and is then transmitted to the wheels, thus causing a so-called creep phenomenon. The creep phenomenon may be very useful under certain conditions, such as when the vehicle that is stopped on an uphill is to be smoothly started, but may be an unnecessary or undesirable phenomenon when the vehicle is to be kept stopped. In the latter case, the vehicle brakes are applied so as to suppress or reduce the creeping force from the engine, resulting in a reduction in the fuel efficiency of the engine.
When the vehicle is in a stopped state in which the brake pedal is depressed to apply the brakes and the acceleration pedal is almost fully released (i.e., the throttle valve is almost fully closed) while the forward drive position is established, it has been proposed to place the transmission in a substantially neutral state while keeping the forward drive position established, in an attempt to improve the fuel economy.
Numerous techniques involving such neutral control and techniques for controlling the brakes during transition from the stopped state to starting of the vehicle have been proposed and disclosed.
For example, Japanese Laid-open Patent Publication No. 7-144625 (JP-A-7-144625) discloses a stop/start control device of a vehicle in which an automatic transmission is installed, which control device reduces as much loss as possible when the vehicle is stopped with the forward drive (D) position established, while automatically applying the brakes during stop of the vehicle, and also realizes a good start of the vehicle after the stop. The stop/start control device includes (a) running condition detecting means for detecting running conditions of the vehicle, (b) the automatic transmission whose shift position is controlled based on the vehicle running conditions detected by the running condition detecting means, (c) braking means for applying brakes to the wheels of the vehicle with the braking force that depends upon the driver's operation of the brake pedal, (d) braking force adjusting means capable of changing the braking force of the braking means independently of the operation of the brake pedal, (e) stop detecting means for detecting the stopped state of the vehicle based on the vehicle running conditions detected by the running condition detecting means, (f) start detecting means for detecting a start of the vehicle based on the vehicle running conditions detected by the running condition detecting means, and (g) a controller that reduces the hydraulic pressure of the automatic transmission while keeping the braking force applied to the wheels at a predetermined value by controlling the braking force adjusting means when the stopped state of the vehicle is detected by the stop detecting means, and returns the hydraulic pressure to a level prior to the reduction while releasing the braking force kept by the braking force adjusting means when the start of the vehicle is detected by the start detecting means.
With the stop/start control device of the vehicle as described above, when a stop of the vehicle is detected by the stop detecting means, the controller reduces the hydraulic pressure of the automatic transmission, and keeps the braking force applied to the wheels at a predetermined value through the braking force adjusting means. If a start of the vehicle is subsequently detected by the start detecting means, the controller resumes the hydraulic pressure of the automatic transmission, and releases the braking force applied to the wheels, through the braking force adjusting means. Since the hydraulic pressure of the automatic transmission is reduced during stop of the vehicle, losses in an oil pump, torque converter and other devices of the hydraulic system can be reduced even if the automatic transmission is placed in the forward drive (D) position during the stop, thus assuring improved fuel economy, and noise due to idling of the engine can also be reduced.
Japanese Laid-open Patent Publication No. 9-202159 (JP-A-9-202159) discloses a braking force control device for a vehicle equipped with a starting clutch, which device prevents the vehicle from moving backward when it is started on a slope. The braking force control device is provided in the vehicle equipped with the starting clutch, wherein the starting clutch is placed in a half-engaged state at an extremely low vehicle speed in the drive position (D range) so that the driving force is given to the vehicle, and the engaging state of the starting clutch is controlled in accordance with the braking operation by the driver (i.e., the driver's operation of the brake pedal), such that the driving force is reduced when the brake pedal is depressed, as compared with the time when the brake pedal is released. The braking force control device includes (a) braking force applying means for applying the braking force to the vehicle irrespective of the driver's operation of the brake pedal, (b) driving force detecting means for determining whether the driving force has changed from a small level to a predetermined large level through driving force control of the starting clutch performed when the brake pedal is released from the depressed state, and (c) braking force control means for controlling the braking force applying means so as to keep the braking force until the driving force detecting means determines that the driving force has reached the predetermined large level.
With the braking force control device as described above, the driving force is controlled to be small when the brake pedal is depressed. When the brake pedal is released from the depressed state, it is determined whether the driving force has been actually increased to a sufficiently large level as a result of the release of the brake pedal, as compared with the previous controlled state in which the driving force was reduced through the driving force control of the starting clutch. Since the braking force control device keeps the braking force until it is determined that the driving force has reached the large level, the vehicle is surely prevented from moving backward upon a start on a slope, without changing the heat resistance of the clutch and the vehicle starting response.
Japanese Laid-open Patent Publication No. 2000-313253 (JP-A-2000-313253) discloses a control device for a vehicle capable of automatically stopping and restarting the engine, which device ensures a good start of the vehicle so that the driver is less likely to feel an abrupt start of the vehicle while preventing the vehicle from rolling or moving backward. The control device is operable when the engine is re-started in the vehicle in which the engine is automatically stopped when certain stop conditions are satisfied, and the engine that was automatically stopped is re-started when certain restart conditions are satisfied. The control device includes (a) holding means for holding the braking force of the vehicle during an automatic stop of the engine, and (b) detecting means for detecting a recovery condition of the driving force of the vehicle upon a restart of the engine, and is characterized by reducing the braking force of the vehicle in accordance with the recovery condition of the driving force of the vehicle when the engine that has been automatically stopped is restarted.
The control device for the vehicle as described above is able to provide appropriate timing of recovery of the driving force and release of the brakes by controlling (reducing) the braking force in accordance with the recovery of the driving force. As a result, the driver is less likely to feel an abrupt start of the vehicle, and the vehicle is prevented from moving backward. The control device also ensures a good start of the vehicle.
Japanese Laid-open Patent Publication No. 11-230327 (JP-A-11-230327) discloses a drive control device of a vehicle, which controls the engagement speed of a clutch when leaving neutral control, in accordance with the level of the driver's demand for starting, thus assuring improved drivability or response to the starting operation of the driver. The drive control device of the vehicle executes neutral control for placing the automatic transmission in a neutral state if predetermined conditions are satisfied even when the forward drive position is selected as the shift position of the automatic transmission, and leaves the neutral control when any of the predetermined conditions is not satisfied. The drive control device includes (a) brake application detecting means for detecting the condition of application of the brakes during neutral control, (b) accelerator position detecting means for detecting the amount of depression of the accelerator pedal, and (c) clutch pressure control means for raising the hydraulic pressure of the clutch when the brakes are released, and increasing the speed of raising the hydraulic pressure as the operating amount of the accelerator pedal increases, based on a signal of the brake application detecting means and a signal of the accelerator position detecting means.
Generally, when the driver performs a starting operation (e.g., when the accelerator pedal is depressed), the driver may wish to quickly start the vehicle, or slowly start the vehicle at a speed slightly higher than the creep speed, or start the vehicle at an intermediate speed. Thus, the driver's demand for starting the vehicle has different levels. With the drive control device of the vehicle as described above, the engagement speed of the starting clutch is varied depending upon the amount of depression of the accelerator pedal. Accordingly, the clutch can be slowly engaged when the amount of depression of the accelerator pedal is small, and can be rapidly engaged when the amount of depression of the accelerator pedal is large. Thus, the drive control device is able to perform appropriate control that meets the driver's demand.
However, the above-described vehicle control performed upon cancellation of neutral control has various problems as follows.
The stop/start control device as disclosed in JP-A-7-144625 only reduces the line pressure during a stop of the vehicle so as to reduce pressure losses in the oil pump and the torque converter even when the forward drive (D) position is selected, to the same extent as in the case where the neutral (N) position is selected. Namely, the engagement pressure of the torque converter is reduced with the reduction of the line pressure, and the vehicle is started while the creep torque is reduced. In this case, if the wheel brakes are not suitably released, the vehicle is not smoothly started, and, for example, the vehicle that is on an uphill may roll or move backward.
The braking force control device as disclosed in JP-A-9-202159 does not involve neutral control. Rather, this control device only places the starting clutch in a half-engaged state in accordance with the braking operation when the vehicle is stopped with the forward drive (D) position selected, and keeps the braking force after a release of the brake pedal until the driving force of the starting clutch reaches a predetermined large level, to thus prevent the vehicle on an uphill from moving backward. Then, the braking force is reduced when the driving force of the starting clutch reaches the large level, which is determined by directly detecting the engagement pressure of the starting clutch or determining that a predetermined time has passed since the engagement pressure of the starting clutch starts being increased. Thus, the braking force is only controlled depending upon the driving force transmitted through the starting clutch, irrespective of how the driver released the brake pedal, or irrespective of the condition of application of the brakes during stop of the vehicle.
In the system in which the engine is automatically stopped during idling, the control device as disclosed in JP-A-2000-313253 holds the braking force of the vehicle during the automatic stop of the engine, and reduces the braking force upon a restart of the engine in accordance with the recovery condition of the vehicle driving force, so as to prevent backward rolling of the vehicle and assure a good start of the vehicle. While the control device as disclosed in this publication may be applied to neutral control, the braking force is controlled only depending upon the driving force of the vehicle, irrespective of how the driver released the brakes, or irrespective of the condition of application of the brakes during the stop of the vehicle, as in the case of the braking force control device as disclosed in JP-A-9-202159.
The drive control device of the vehicle as disclosed in JP-A-11-230329 merely raises the hydraulic pressure of the clutch when the brakes are released upon return from neutral control, and also increases the speed of raising the hydraulic pressure as the operating amount of the accelerator pedal increases, so as to improve drivability or response to the starting operation of the driver. While the clutch pressure can be controlled in accordance with the operation of the accelerator pedal by the driver, the control device disclosed in this publication is not arranged to perform control in accordance with the braking operation of the driver (e.g., the braking operation during neutral control and the brake releasing operation at the time of cancellation of neutral control).